1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to an aramid fiber cord for use as a load carrying component in a power transmission belt and having excellent resistance to elongation, flexing fatigue, and fraying.
2. Backqround Art
It is known to use aramid fiber cords as load carrying members in power transmission belts. The aramid fiber is an organic fiber that is strong and flexible and has good dimensional stability in high temperature environments as compared to other organic fibers. One drawback with load carrying cords made of aramid fiber is that the fibers have a tendency to fray. This is particularly a problem in belts in which the laterally oppositely facing drive/driven surfaces are exposed, i.e. do not have any covering layer, such as canvas, thereon. This situation is common in synchronous belts, V-ribbed belts, and V-belts. Fraying may occur at manufacture and/or during use as the exposed cords on the laterally facing surfaces repeatedly contact and disengage from a cooperating pulley.
Attempts have been made to alter the characteristics of the aramid fiber to make cords constructed therefrom more suitable as a component in a power transmission belt. It is known, for example, to treat the cords with a resorcinol formalin rubber latex adhesion liquid (hereinafter RFL liquid). Cords so treated have good bending strength, however are still prone to fraying.
It is also known to pre-treat the cords with epoxy or isocyanate compound before treatment with the RFL liquid. This results in the hardening of the cord, which alleviates much of the fraying problem. However, the hardened cord has less resistance to flexing fatigue than the cord does in the absence of this treatment. Accordingly, neither of the above treatments satisfactorily addresses both the problems of fraying and flexing fatigue.
One of the inventors herein, together with employees of the assignee of this invention, previously invented a manufacturing method in which the aramid fiber is treated with a mixture of epoxy compound, including at least one epoxy radical, and liquid rubber. The treated fibers are then adhesively vulcanized with unvulcanized rubber. While this method significantly improves the resistance of the aramid fibers to both flexing fatigue and fray, the adhesion between the fibers and rubber layer, in which they embed, has not proven as effective as desired. Consequently, there remains a need to develop a cord with excellent resistance to both fray and flexing fatigue and one which is effectively adhered to the rubber component layer of a power transmission belt in which it is embedded.